Ultraviolet light stabilizers for plastic materials



United States Patent ULTRAVIOLET LIGHT STABILIZERS FOR v PLASTIC MATERIALS Hans Dressler, Pitcairn, and Kenneth G. Reabe, Delmont, Pa., assignors to Koppers Company, Inc., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 647,281, May 1, 1967, which is a division of application Ser. No. 375,968, June 17, 1964, now Patent No. 1 3,352,896, dated Nov. 14, 1967. This application Nov. v30, 1967, Ser. No. 687,964

6 Claims. (Cl. 260-4535) ABSTRACT OF THE DISCLOSURE Bis(3-hydroxy-4-benzoylphenoxy) diphenyl silane and bis(3-hydroxy-4-benzoylphenoxy) dialkyl silane stabilize polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl chloride, copolymers of vinylidene chloride and vinyl chloride, nitrocellulose, ethyl cellulose, cellulose acetate and polyester resins against ultraviolet light degradation. The stabilizer is generally added in an amount of between 0.01 and 5 percent by weight of the plastic material.

Cross-reference to relation applications This application is a continuation-in-part of application, Ser. No. 647,281, filed May 1, 1967, now abandoned, as a division of application, Ser. No. 375,968, filed June 17, 1964, now U.S. Patent No. 3,352,896, issued Nov. 14, 1967.

Background of the invention This invention relates to ultraviolet light stabilizers for plastics. In one specific aspect it relates to plastic compositions stabilized against degradation resulting from exposure to ultraviolet radiation.

It iswell known that many plastic materials tend to undergo deterioration upon exposure to ultraviolet radiation. Light having wave lengths of about 290-400 millimicrons causes photocatalyzed changes, such as yellowing or embrittlement, in unstabilized polymers. This is particularly undesirable for colorless translucent and transparent plastics which are required to withstand long exposure to intense sunlight. To overcome this problem, it is usually necessary to stabilize plastics, such as for use in translucent roofing, transparent structures, protective coatings, impact resistant windows and decorative structures, which are subjected to prolonged exposure to ultraviolet radiation.

In recent years, organic compounds have become available which can absorb ultraviolet light and convert it to less harmful forms of energy such as heat, vibrational energy or less harmful radiation. These organic stabilizers, in addition to absorbing ultraviolet radiation in the selected range for the plastic material being treated, must be compatible with the plastic, have little or no initial color, be reasonably inexpensive, be chemically stable, and have a low toxicity especially for stabilizing plastics used in the food industry.

As a general rule, an effective ultraviolet light stabilizer should have a molar extinction coetficient (e) of about 10,000, that is, the log 6 of the molar extinction coeflicient is equal to or greater than 4.0 in the 300-400 millimicron spectral region to have potential value as an ultraviolet light stabilizer for plastics. However, individual plastics are generally most susceptible to deterioration by radiation of particular wave lengths. Thus, polyethylene and polystyrene are susceptible to radiation having a wave length of 300-320 millimicrons, while polypropylene is 7 most sensitive to radiation at 370 millimicrons. One disice advantage of presently available commercial stabilizers is that their extinction coefiicient is too low over a broad band in the ultraviolet light region to be etfective'for general use. i

' Summary ofthe invention Quite surprisingly we have discovered that certain organic silane derivatives are compatible with a large number of plastic materials and exhibit outstanding ultraviolet light absorbing properties over awide range. These compounds do not impart any substantial color to transparent colorless plastics.

It is, therefore, an object of the present invention to provide a novel composition which is resistant to degradation by ultraviolet radiation.

It is another object of the present invention to provide plastic compositions containing the novel organic silane derivatives which are substantially resistant to ultraviolet deterioration.

In accordance with the present invention, we have dis covered that derivatives of bis(3-hydroxy-4-benzoylphenoxy) silane are particularly useful as ultraviolet light stabilizing agents for plastic materials.

These compounds have the formula:

HO OH Eli 3 A l.

wherein R is a member selected from the group consisting of phenyl and alkyl having from l-l2 carbon atoms. The compounds of the present invention are particularly compatible with polyethylene and polypropylene and give excellent stabilization of these plastics against deteriorating effects of ultraviolet light without causing any substantial discoloration of the plastics.

Detailed description The novel ultraviolet light stabilizer can be readily incorporated into the plastic material by various standard procedures. In one technique, the dry stabilizer in powdered form is mixed with a powdered or granular plastic and the mixture is then appropriately treated by molding or extruding. In another procedure an aqueous suspension or emulsion of finely divided polymeric material may be admixed with a suspension or emulsion of the stabilizing agent. Alternatively it is possible to spray or mix a polymeric material in powdered or granular form with a solution or dispersion of the ultraviolet light absorbing agent in an appropriate solvent such as hexane or benzene. It is also possible to incorporate the ultraviolet absorbing agent in a finished article by introducing the plastic material into a bath containing the ultraviolet light absorbing agent in an appropriate liquid solvent and permitting the plastic material to remain in the bath for some time until the plastic has been properly treated. Thereafter, the material is dried to remove any of the remaining solvent. Plastic material in the form of fibers and film's may also be sprayed with a solution or suspension of the agent absorbing ultraviolet rays in a solvent or dispersant by any standard technique.

The plastic material should contain a stabilizing amount of the ultraviolet light absorbing agent, that is, the amount of stabilizing agent sufiicient to prevent deterioration and embrittlement of the plastic material. The amount of stabilizing agent to be used will depend to a large extent upon the amount of exposure to which plastic is subjected and the nature of the plastic to be treated. The agent is generally added in an amount of between 0.01 and 5 percent by weight of the plastic material and preferably between 0.1 to 4 percent by weight.

The stabilizing agent imparts protection against ultrasenitive to ultraviolet light. Theseinclude, for example,

clear films made of polyvinyl chloride and cellulose acetate which are used in packaging dye textile articles and automobile seat covers. The agent also protects resins used, for example, in the preparation of glass fiber reinforced structure panels which are subject to discoloration on outdoor exposure.

The term polyester resin as used herein is intended to define the combination of an u,B-ethylenically unsaturated copolyrnerizable monomer such as styrene and the esterification product of adicarboxylic acid or its anhydride, atleast a portion of which contains ethylenic unsaturation, condensed with a'dihydricalcohol.

Examples of' such dicarboxylic acids include orthophthalic acid and its halogenated homologs, tetrahydrophthalic anhydride, hexahydrophthalic anhydride and the like. A typical ethylenically unsaturated dicarboxylic acid is maleic acid. Examples of dihydric alcohols include ethylene glycol, propylene glycol, butylene glycol and the like.

The ultraviolet stabilizer is particularly effective for protecting polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl chloride, copolymers of vinyl chloride and vinylidine chloride, cellulose resins such as nitrocellulose, ethylcellulose and cellulose acetate and numerous other materials. One outstanding property of the stabilizing agent is its heat stability making it particularly desirable when high molding or extrusion temperatures are required, e.g., for polycarbonates. The agent can be used alone or together with other additives such as fillers, antioxidants, pigments, etc.

The invention will further be illustrated in the following examples.

Example I A mixture of 10.7 g. (0.05 mole) of 4-benzoylresorcinol, 6.3 g. (0.025 mole) of diphenyldichlorosilane, and 80 ml. of benzene was refluxed in a nitrogen atmosphere. After 8 hours the initially brisk evolution of HCl had nearly ceased. On cooling and standing, 1.2 g. of 4-benzoylresorcinol (11 percent recovery) crystallized from the yellow solution, and was filtered off and dried (M.P. and mixed M.P. 141-5 C.).

The filtrate was washed with two 50 ml. portions of water and extracted with 50 ml. of 5 percent aqueous sodium carbonate solution. Acidification of the sodium carbonate extract precipitated 1.1 g. (10 percent recovery) of unreacted 4-benzoylresorcinol (M.P. 145-7" 0.).

The organic phase was washed with 50 ml. of water, dried over magnesium sulfate, filtered and the solvent was evaporated on the steam bath. A viscous light yellow oil weighing 13.2 g. (86 percent yield) was obtained. The product exhibited infrared absorptions consistent with the structure, bis(3-hydroxy-4-benzoylphenoxy)diphenylsilane.

Example 11 A mixture of 10.7 g. (0.05 mole) of 4-benzoylresorcinol, 6.3 g. (0.025 mole) of diphenyldichlorosilane, and 80 ml. toluene as the solvent and increasing the reflux time to 24 hours, after which no further hydrogen chloride evolution was detected. The toluene was distilled off at atmospheric pressure to a pot temperature of 150 C. A small amount of HCl liberation was noticeable, and the residue was heated for two hours at 150-200" C. until no further HCl was envolved.

On cooling the residue (13.5 g., 88 percent yield) set to a pale, brittle, resinous solid (M.P. 60-65 C.). The infrared spectrum of the resinous solid was identical to that of Example I. The product, bis(3-hydroxy-4-benzoylphenoxy)diphenylsilane had a log 6 (molar extinction coefficient) equal to or greater than 4.0 in the spectral region of 290-298 and 311-343 millimicrons.

.4; Example III The product of Example II, bis(3-hyd-roxy-4-berizoylphenoxy)diphenylsilane, was tested to determine its ability to stabilize polystyrene against ultraviolet light degradation. The stabilizer in varying amounts was blended with 100 parts of-polystyrene. beads by rolling in a jar mill. The stabilized beads audit-control sample were extruded into pelle ts'from which discs=2 inches-in diatrieter and A; inch thick were molded by'injec'titinjnolding. These molded discs were then exposed'to 'ultraviolet radiation under a 325 watt H anoy'ia lar'npffor 12 0 ou'r s. A Yellowness Index, which. represents the relatigedegree of yellow coloratiombased upon spectrophotom tric analysis was determined for the samples of eachi ofythe compositions. The difference in the-'Yllowness Index before and after exposure or the amount of discoloration caused by the ultraviolet radiation is designated as the Yellowness Factor:-Results of-the test are' given in the table below.

' One part of bis(3-hydroxy-4-benzoylphenoxy)diphenylsilane was blended with 100 parts of low density polyethylene and 0.05 part 4,4'-thio-bis'(6-t butyl m-cresol7 by milling on a two run mill at 320 F. for five minutes. The clear thin films, 0.05 mm. thick, were molded from the stabilized resin and visual inspection indicated that the resin and the stabilizer were completely compatible. These films were exposed for 500 hours to the light of an ultraviolet lamp. The stabilized films remained substantially unchanged and no embrittlement could be ascertained while the unsta-bilized film showed discoloration and embrittlement.

Similar results are obtained when polypropylene; copolymers of vinylidine chloride and vinyl chloride, or styrene modified mal'eic glycol polyesters are used inthe foregoing example. i

Example V A mixture of 10.7 g. (0.05 mole) of 4-benzoylresorcinol, 8.13 g. (0.025 mole) of di-n-octyldichlorosilane and ml. of toluene were stirred and refluxed 'in'a nitrogen atmosphere for 24 hours, after which time no further evolution of hydrogen chloride could be detected. The toluene was distilled off to' a temperature of'1'50 C. and the residual massheated'under'full aspirator vacuum for 4 hours on a steam bath. The residual viscous oil exhibited infra-red absorptions consistentwith his 3 -hydroxy-4-benzoylphenoxy') di-n-ac'tylsilane;

The product when incorporated'in an amount of 0.01-5- One part by weight of bis(3 hydroxy-4-benzoylphe noxy)diphenylsilane was blended into 200 parts by weight of a. polyester resin made bycondensing hexahydrm phthalic anhydride and maleic anhydride withethylene glycol and butylene glycol-and dissolving theresulting condensation polymer in monomeric styrene to a.60:4 0 polymerzmonomer ratio.

To this mixture was added 1% by weight benzo yli peroxide catalyst to copolymerizc the mixture and clear castings measuring 8 x 8" x sf were,.cas,t; fr.oru the mixture and cured for 1 /2 hours at 60 C. followed by 1 hour at 90 C. and then 2 hours at 150 C. The samples were then exposed to ultraviolet light radiation from a 32.5 watt Hanovia lamp for 1,000 hours together with blank samples prepared but omitting the stabilizer of the invention. The blank samples had a yellowness factor of 15.3 while the samples containing the bis(3-hydroxy-4-benzoylphenoxy)diphenylsilane had a yellowness factor of 0.9.

We claim:

1. A polymeric composition stabilized against ultraviolet degradation comprising a polymer selected from the group consisting of polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl chloride, copolymer of vinylidene chloride and vinyl chloride, nitrocellulose, ethyl cellulose, cellulose acetate, and polyester resins having incorporated therein a stabilizing amount of a compound having the formula:

wherein R is a member selected from the group consisting of phenyl and alkyl having from 1-12 carbon atoms.

2. The polymeric composition of claim 1 wherein the amount of stabilizer is 0.01 to 5 percent by weight of said polymer.

3. The composition of claim 1 wherein the polymer is polystyrene and the stabilizer is bis(3-hydroxy-4-'benzoylphenoxy)-diphenyl silane.

4. The composition of claim 1 wherein the polymer is polyethylene and the stabilizer is bis(3-hydroxy-4- benzoylphenoxy)-diphenyl silane.

5. The composition of claim 1 wherein the polymer is polypropylene and the stabilizer is bis(3-hydroxy-4 benzoylphenoxy)-diphenyl silane.

6. The composition of claim 1 wherein the polymer is a polyester resin and the stabilizer is bis(3-hydroxy-4- benzoylphenoxy)-diphenyl silane.

References Cited UNITED STATES PATENTS 8/1960 Bailey et al 260' 448;8 8/1966 Holub 260-448.8 

